For the use of motor vehicles which are more environmentally friendly, various alternatives to the conventional internal combustion engine, for example the use of hybrid drives, are known.
A further option for reducing consumption is a so-called “coasting function”, also referred to as a “free-wheeling function” which is used in order to reduce the energy consumption in predetermined driving states by the drive being switched off and the automatic transmission being shifted into the neutral position or with the clutch open.
In previous coasting driving strategies, the following approaches have been taken. In a first strategy, the gear from the traction phase before the coasting was retained. In a sporty driving mode, i.e. at a low gear, a large jump in rotational speed may occur, since the selected gear is too low when driving downhill with an increase in velocity. Furthermore, the gear may no longer be appropriate after a long coasting phase and after steady driving and then greater acceleration being required. In the latter case, the gear would be too high, i.e. the traction force would be too low, and re-shifting would be necessary. A second strategy involves engaging the highest possible gear. The gear is not appropriate in a normal to sporty driving mode. It is too high, i.e. the traction force is too low, and therefore re-shifting is necessary. A third strategy envisages tracking of the gear after the normal shifting program taking into consideration the sporty factor of the transmission. This is possible during coasting with a gas pedal value>0, but the gear selection is often implausible. During coasting with a gas pedal value of 0, the shifting program is not appropriate.
DE 103 27 438 A1, which is incorporated by reference, describes a method for controlling and/or regulating a transmission, wherein a means of preventing up shifting can be deactivated in the “coasting function active” operating state. The described up shifting strategy during the coasting operation indicates that, after the ending of the coasting function, a predeterminable shifting characteristic can be selected.
It is therefore an object of the present invention to provide an improved gear selection method and an improved gear selection device for an automatic transmission for a traction phase after a coasting phase of a motor vehicle, the method and device permitting good adaptability to the driver's dynamic strategy.